Nitrocellulose lacquer compositions



, Patented Sept. 18, 1945 mrnocsLLULosn LACQUER comosrrioss Gerald R.Barrett, Winchester, Mass, assignor to Monsanto Chemical Company, St.Louis, Mo., a

corporation of Delaware Application December 31, 1942,

Serial No. 470,901 9 Claims. (01.106481) aration oi nitrocelluloselacquer compositions having a markedly decreased tendency to gel.

It is well known that nitrocellulose lacquers containing as pigmentscertain metal constitue v ents, such as, bronze, aluminum-bronze,goldbronze or other copper-containing powders or pastes, are subject torapid gelation or livering Moreover, these lacquers tend to becomegelled or gelatinized in the presence oi. lead powders or pastes,andveven in the" absence of metal powders, when they are packaged inlead-lined or lead containers, such as collapsible tubes or lead toll.

It is accordingly a primary object of the present invention to provideinhibiting agents, which when added to nitrocellulose lacquers in smallquantities will markedly reduce or completely prevent any tendencytoward gel formation.

A further object the invention is to provide an, inhibiting agent or thetype described which is more effective than most, if not all previouslyknown inhibiting agents.

Still further objects and advantages oi the invention will appear fromthe tollowing description and appended claims. Before explainingindetail the present invention, however, it is to be understood that theinvention is not limited in its application to the details describedherein, since ,the invention is capable of other embodiments and ofbeing practiced or carried out in various ways;

The invention is carried out in general by incorporating in the usuallacquer formulations; either containing bronze or other similar powdersor intended to be" packaged in lead lined or like containers, smallamounts of a certain polycarboxylic organic acid. Although malic,citric, tartaric and other polycarboxylic organic acids have been usedpreviously for this purpose, these acids are not as efl'ective as theparticular acid which is the subject of this invention.

According to this invention the most suitable polyca'rboxylic organicacid for obtaining maximum prevention or reduction in gelation ismelonic acid. This acid is so effective that it ma sometimes be used inamounts as small as 0.01% by weight based onthe weight of the clear orpigmented lacquer being treated. In general, however, it is preferableto employ amounts of the acid varying from 0.05 to 1% based on thelacquer solution, either pigmented or otherwise. In some cases, it isdesirable to use amounts oi acid as large as 5%. but in most instancesconcentrations as large as this are to be avoided, as these largeramounts have a tendency to crystallize from the lacquer film and theyalso decrease the water'resistance oi the film.

In general the presence of copper or lead is the chief cause of gelationin nitrocellulose lacquers, that is bronzes or other metal powders highin copper or lead are most apt to cause gelation. For this reason,relatively large amounts of the malonic acid are usually required in thecase of lacquers containing powders or pigments which are high in copperor lead. Only relativelysmall amounts of the malonic acid are required,on the other hand, in the case of clear lacquers which are subjected tothe undesired action of metals merely by being packaged in metalcontainers, due to the considerably smaller surface area to which thelacquer. is exposed in such instances.

A further understanding of the invention will be obtained from thefollowing examples,

Bramble I A clear lacquer base 01' the following 0 mp0- sition was firstprepared:

Percent by weight Cellulose nitrate (/2 second viscosity) 25 Butylacetate 31 Toluene L.-- 30,6 Denatured alcohol 13 Malonic acid; 0.4

Twelve parts of gold bronze. were added to parts of the above clearlacquer. Upon packag ing samples of the clear lacquer and thebronzecontainlng lacquer, as well as samples of the above clear lacquerwith the malonic acid omitted, in lead containers, it was found that thelacquers containing the malonic acid, either with or without addition01' the gold bronze, were more resistant to gelation than similarlacquers which i were free oi malonic acid.

' Example II Aclear lacquer base of theri'ollowing composition was firstprepared:

Per cent by weight Celluloid scraps Acetone 36 Petroleumlacquer diluent14 Denatured. alcohol.- 35

sition resisted gelation for two months, while gelation set in alteronly three days when an equal quantity of malic acid was employed. Inthe absence of the lead paste, but with the compositlon ltored in a leadlined container the above amount of malonic acid appeared adequate toprevent gelation indefinitely,

Example II! To 100 parts of a clear lacquer base having the followingcomposition:

Per cent by weight were added 5 parts of copper lining powder. In theabsence of inhibitor the above lacquer composition gelled in a fewhours. Upon adding 0.1 part of malonic acid to an equal amount of theabove powder-containing lacquer, the composition remained fluid afterthree months, while the addition of 0.1 part of malic acid to an equalamount of powder-containing lacquer only delayed gelation for threedays.

Similar tests on a lacquer composition similar to the above but withlead paste substituted for the copper lining powder also indicated thatmalonic acid is superior to malic acid as an effective inhibitor ofgelation.

Emmple IV To a clear lacquer base having the following composition:

Per cent by weight Nitrocellulose (15 seconds viscosity) 8 Ethyl acetatel Butyl acetate 20 Butyl alcohol 10 Ethyl alcohol 10 Toluene 34 Ester gDibutyl phthalate 3 were added 13 parts of fine copper bronze. In theabsence of inhibitor the resulting composition gelled in a few hours.Upon adding 0.4% of malonic acid (based on the clear lacquer) to thecomposition, it remained fluid after aging it for a month, while asimilar test with malic acid substituted for the malonic acid showedpartial gelation at the end of one month.

Although the examples refer solely to the treatment and testing of clearlacquers and lacquers containing various metal powders or pastes, themethods of this invention are also applicable to lacquers containingother forms of pigment, whether packaged in lead or lead-linedcontainers or otherwise. In general, the most difficult problems ofgelation occur with lacquers containing copper-containing orlead-containing powders or pastes of the type referred to in theexamples, but the advantages of the invention are also applicable toother types of lacquers, particularly when they are packaged in lead orlead-lined containers.

Where reference is made herein and in the appended claims to bronzepowder, it is to be understood that this includes metal powder or flakeof such materials as brass, aluminum, lead or copper, and the usualcopper-tin or copper-zinc alloys. In some instances, reference is madeto metal pastes. These are merely mixtures of metal, i. e. bronze powderwith suitable organic solvents, and in some instances, with a polishingor leaflng agent, such as stearic acid.

Although the reason for the beneficial action of malonic acid uponlacquers of the type described is not definitely known, it is believedthe malonic acid functions as a preventive of gelation by causing theformation of a thin protective film of insoluble metal malonate on thesurface of the metal in contact with the lacquer. This film stifiesfurther corrosion and prevents the building up of a concentration ofdissolved metal ions capable of reacting with the nitrocellulose to formthe material causing gelation. For example, dissolved lead salts, suchas lead naphthenate, react instantly with a nitrocellulose solution toform a gel. Copper salts, on the other hand, do not so react, butinstead require the presence of metal powder to cause gelation. Whateverthe cause of gelation, however, it is believed the malonic acidfunctions by virtue of its ability to form a metal malonate which isinsoluble in the lacquer solution.

What I claim is: g

A substantially non-gelling nitrocellulose lacquer containing from 0.01to 5% by weight of malonic acid based on the total weight of the lacquerprior to the addition of said acid, said lacquer having a tendency togel in the absence of said acid.

2. A substantially non-gelling nitrocellulose lacquer containing from0.05 to 1% by weight of malonic acid based on the total weight of thelacquer prior to the addition of said acid, said lacquer having atendency to gel in'the absence of said acid.

3. A substantially non-gelling nitrocellulose lacquer containingnitrocellulose, a solvent mixture, metal powder, and from 0.01 to 5% byweight of malonic acid based on the total weight of the lacquer prior tothe addition of said acid, said lacquer having a tendency to gel in theabsence of said acid.

4. A substantially non-gelling nitrocellulose lacquer containingnitrocellulose, a solvent mixture, metal paste, and from 0.01 to 5% byweight of malonic acid based on the total weight of the lacquer prior tothe addition of said acid, said lacquer having a tendency to gel in theabsence of said acid. Y

5. A substantially non-gelling nitrocellulose lacquer containingnitrocellulose, a solvent mixture, a. bronze powder, and from 0.01 to 5%by weight of malonic acid based on the total weight of the lacquer priorto the addition of said acid, said lacquer having a tendency to gel inthe absence of said acid. a

6. A substantially non-gelling nitrocellulose lacquer containingnitrocellulose, a solvent mixture, lead paste, and from 0.01 to 5% byweight of malonic acid based on the total weight of the lacquer prior tothe addition of said acid, said lacquer having a tendency to gel in theabsence of said acid.

'7. The method of preventing orreducing gelation in a nitrocelluloselacquer containing a metal powder of the type tending to cause gelationwhich comprises addingto said lacquer from 0.01 to 5% by weight ofmalonic acid based on the total weight of the lacquer.

8. The method of preventing or reducing gelation in a nitrocelluloselacquer containing a metal paste of the type tending to cause gelationwhich comprises adding to said lacquer from 0.01 to 5% by weight ofmalonic acid based on the total weight of the lacquer.

9. The method of preventing or reducing gelation in a nitrocelluloselacquer which is packaged in a lead or lead-lined container whichcomprises adding to said lacquer from 0.01 to 5% by weight of malonicacid based on the total weight of the lacquer.

GERALD R. BARRETT.

